I read somewhere that as a rule, young guinea pigs don't like a variety of food. Mine is maybe 6 months, and she isn't fond of variety either. The most important thing is that she eats enough hay, and either pellets or some other nutritious food like a supplement of Critical Care, to make sure she gets the nutrients she needs. In addition, vitamin C is important, and at her age, a little extra calcium which could come from dark green leafy veggies, alfalfa, or young guinea pig pellets.
As far as drinking water, I'm assuming you've tried a water saucer or cup that's heavy so it can't be tipped, or a smaller size water bottle that she can get her mouth around. The other option is to give leafy veggies dipped in water, or draped over the side of a water saucer.
You should be able to tell if she's eating enough by tracking her weight and by her output. At her age she should gradually increase in weight, but I've noticed with mine she stays about the same for a few days, maybe drops a few grams one day, then gains a few grams. The trend should continue to show an increase overall.